What is C, and why learn it?
Where C came from, where it runs today, and how a C program goes from text to something your computer can execute.
- Explain what C is and name places it is used today
- Describe the compile step: source code in, executable out
- Tell the difference between a compiled and an interpreted language
C is a small, fast, general-purpose programming language. It gives you a thin, predictable layer over what the hardware actually does: memory is a long row of numbered bytes, and your program reads and writes them. That closeness to the machine is exactly why C is still everywhere, fifty years after it was created.
Where C came from
C has been standardized several times since. You will see these names: C89/C90 (the first standard), C99 (added // comments, bool, declaring variables anywhere), C11, C17 (bug fixes), and C23 (the newest). This track uses modern C17, which every current compiler supports.
Where C runs today
You use software written in C every day, usually without noticing:
- Operating systems: the Linux kernel, most of Windows' and macOS's low-level parts.
- Embedded devices: microwaves, cars, routers, pacemakers, anything with a microcontroller.
- Language runtimes: the main Python interpreter (CPython), Ruby, PHP and Lua are written in C.
- Databases and servers: SQLite, PostgreSQL, Redis, nginx.
- Games and graphics: engines and drivers where every millisecond counts.
Learning C teaches you how computers actually work - memory, pointers, how data is laid out - and that knowledge transfers to every other language you will ever use.
From source code to a running program
C is a compiled language. You write source code in a plain text file ending in .c. A program called a compiler (such as gcc or clang) reads it and translates it into machine code - the raw instructions your processor runs - and saves that as an executable file.
Under the hood the compiler works in stages:
- Preprocessing: handles lines starting with
#, like#include <stdio.h>, by pasting in other files. - Compiling: turns your C into assembly, then into machine code (an object file).
- Linking: joins your object file with library code (like the code behind
printf) into one executable.
On Linux or macOS, compiling and running a program looks like this in a terminal:
$ gcc -Wall -o hello hello.c
$ ./hello
Hello, world!gcc is the compiler, -Wall turns on helpful warnings, -o hello names the output file, and hello.c is your source. Then ./hello runs the program you just built. In this track you do not need to install anything: code examples and exercises compile and run right here on the page.
What makes C different
C is famous for trusting the programmer. That has good and bad sides:
| C gives you | C expects from you | | --- | --- | | Direct access to memory through pointers | Never reading or writing memory you do not own | | Very fast, very small programs | Managing memory yourself (no garbage collector) | | Portability to almost any hardware | Checking errors - C will not stop you |
This track will teach you both halves: the power, and the habits that keep that power safe.
Key takeaways
C was created at Bell Labs in the early 1970s to write Unix, and is still used for operating systems, embedded devices, databases and language runtimes.
C is compiled: a compiler such as
gccturns.csource into a machine-code executable in stages - preprocess, compile, link.C gives you direct control over memory and expects you to use it carefully.
Lesson quiz
5 questions · pass with 4 correct · up to 50 XP
Passing this quiz completes the lesson and keeps your streak going. Questions you miss come back in review sessions later.
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